For database items that can raise alarms, every situation or ‘condition’ that can raise an alarm (such as a change in point state, or an outstation losing communications) is associated with an Alarm Condition. An alarm condition identifies the particular abnormal occurrence that has triggered the alarm (for instance, a ‘Point State’ condition indicates that a change in point state has caused an alarm to be raised). An alarm condition becomes active when the item enters a state for which an Alarm Severity is configured. An alarm condition becomes inactive once the item is no longer in a state for which an Alarm Severity is configured and the alarm that has cleared as a result of this change has been acknowledged. The ‘normal’ state of an item is deemed as inactive with respect to alarm conditions and alarm subconditions.
Example:
A point has states High, Normal, and Low, where High and Low are configured as alarm states. Whenever the point value rises above the High limit, the point changes to the High state and the point's 'Point State' alarm condition becomes active. Whenever the point value falls below the High limit, the point changes to the Normal state and the alarm condition becomes inactive.
Similarly, if the point value falls below the Low limit, the point changes to the Low state and the point's 'Point State' alarm condition becomes active. Whenever the point value rises above the Low limit, the point changes to the Normal state and the alarm condition becomes inactive.
Each alarm condition comprises at least one Alarm Subcondition. A subcondition is a particular class of alarm condition. The active subcondition provides an indication of the cause or ‘state’ of the alarm (such as an analog point’s value exceeding the High limit). Some alarm conditions comprise multiple alarm subconditions, with each subcondition representing one of the alarm’s possible states. An alarm condition can only have one active subcondition at any time.
Example:
A point has states High High, High, and Normal, where High High and High are configured as alarm states. The point’s ‘Point State’ alarm condition is active whenever the point value is above the High limit, and inactive when below the High limit. Additionally, the High and High High states each have their own alarm subcondition (there is no active subcondition when the point is in the Normal state).
So, whenever the point is in the High state, both the ‘Point State’ alarm condition and the High state’s alarm subcondition are active. If the point value then rises above the High High limit, the alarm condition remains active. Additionally, the active subcondition changes from the High state’s subcondition to the High High state’s subcondition.
When the Multiple Point State Alarms feature is being used (see Multiple Point State Alarms in the ClearSCADA Guide to Core Point Configuration), each point will have several 'Point State' alarm conditions, each with the same subconditions. The mapping between the point's states and the alarm conditions is then configurable on a point-by-point basis, so several conditions may be active at any given time.
Further Information
Include information about alarm conditions and subconditions in alarm redirection messages: see Use Trip Sequences to Include Alarm Condition and Subcondition Details in the ClearSCADA Guide to Alarm Redirection